Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a first image of a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design; and,

FIG. 2 is a second image thereof.

The broken lines shown in the figures depict portions of the display screen or portion thereof with transitional graphical user interface that form no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-2. The process, or period, in which one image transitions to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 